23 July 2012

Artificial jellyfish shows new route to synthetic organisms

by Will Parker

Using only silicon and cultured rat heart muscle tissue, bioengineers from Caltech and Harvard University have created a jellyfish-like creature that, despite its relative simplicity, shows complex swimming and feeding behaviors.

The researchers say the creature - dubbed a medusoid - serves as a proof of concept for reverse engineering a variety of muscular organs and simple life forms. They argue that it also suggests a broader definition of what counts as synthetic life in an emerging field that has predominantly focused on replicating life's basic building blocks. The techniques used for building the creature are detailed in Nature Biotechnology.

The bioengineering approach used by the team is the opposite of most other nascent artificial organism construction techniques. "In many ways, it is still a very qualitative art, with people trying to copy a tissue or organ just based on what they think is important or what they see as the major components - without necessarily understanding if those components are relevant to the desired function or without analyzing first how different materials could be used," explains Caltech's Janna Nawroth. "Because a particular function - swimming, say - doesn't necessarily emerge just from copying every single element of a swimming organism into a design, our idea was that we would make jellyfish functions - swimming and creating feeding currents - as our target and then build a structure based on that information."

To create the medusoid, the team used analysis tools borrowed from the fields of law enforcement biometrics and crystallography to make maps of the alignment of subcellular protein networks within all of the muscle cells within a real medusa jellyfish. They then conducted studies to understand the electrophysiological triggering of jellyfish propulsion and the biomechanics of the propulsive stroke itself.

As it turned out, they found a sheet of cultured rat heart muscle tissue that would contract when electrically stimulated in a liquid environment was the perfect raw material to create the ersatz jellyfish. The researchers then quantitatively matched the subcellular, cellular, and supracellular architecture of the jellyfish musculature with the rat heart muscle cells. The final step was incorporating a silicone polymer that fashions the body of the artificial creature into a thin membrane that resembles a small jellyfish, with eight arm-like appendages.

When the researchers set the medusoid free in an electrically conducting container of fluid (resembling ocean water) and oscillated the voltage from zero volts to five, they shocked the creature into swimming with synchronized contractions that mimic those of real jellyfish. Intriguingly, the researchers report that the muscle cells started to contract slightly on their own even before the electrical current was applied.

"I was surprised that with relatively few components - a silicone base and cells that we arranged - we were able to reproduce some pretty complex swimming and feeding behaviors [creating feeding currents] that you see in biological jellyfish," says Caltech's John Dabiri, citing fluid-dynamics measurements that match up to those of the real animal. "I'm pleasantly surprised at how close we are getting to matching the natural biological performance, but also that we're seeing ways in which we can probably improve on that natural performance. The process of evolution missed a lot of good solutions."

The medusoid, the team says, demonstrates that it is inadequate to simply mimic nature: the focus must be on function. Their design strategy, they suggest, will be broadly applicable to the reverse engineering of muscular organs in humans.

Looking forward, the researchers aim to further evolve the artificial jellyfish, allowing it to turn and move in a particular direction, and even incorporating a simple "brain" so it can respond to its environment and replicate more advanced behaviors like heading toward a light source and seeking energy or food. "We're reimagining how much we can do in terms of synthetic biology," said Dabiri. "A lot of work these days is done to engineer molecules, but there is much less effort to engineer organisms."

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Source: California Institute of Technology, Harvard University